How to record stereo with AT-2020 mic

I’m using an AT-2020 mic with a MobilePre interface trying to record stereo on Audacity, but for some reason it’s only recording either the right or left side depending on which port I plug the mic into on the MobilePre.

I’m trying to figure out whether it’s the mic, MobilePre or possibly the computer.

Maybe it’s because you only have one mic?